The present invention relates to a process for the manufacture of a pane of laminated glass comprising at least one external layer of glass and at least one interlayer of thermoplastic polymer, in which the various layers are stacked, the pack of layers is put under vacuum in a vacuum box for the purpose of extracting gas from the spaces separating the layers and, finally, the pack of layers, the edge of which is sealed, is brought to atmospheric pressure and its temperature increased. The invention also relates to an apparatus for the implementation of the process according to the invention.
Hitherto, it was standard practice, in the manufacture of laminated glass, to produce beforehand a primary laminate, based on the stack of layers, by means of a calendering operation or a vacuum treatment so as to extract, to a large extent, the air trapped between the layers, and subsequently to subject this primary laminate to a high overpressure, generally of between 10 and 14 bar, in an autoclave. These so-called autoclaving processes are expensive and tiresome.
Processes for manufacturing laminated glass are also known in which an autoclaving operation is not essential for the final bonding, rather the latter is carried out at atmospheric pressure. A process of this type has been described, for example, in document DE3,044,717 C2. According to this known process, a rubber frame is laid around the edge of the pack of layers, which frame is provided with a suction channel which is continuous and comprises a suction line. The pack of layers fitted with this rubber frame is placed in a vacuum box and the suction line is brought to the outside through the wall of the box. Then, a different high vacuum is applied, on the one hand, to the spaces separating the various layers, by means of the suction line and the rubber frame, and, on the other hand, to the box in such a way that, under the effect of the vacuum in the vacuum box, the layers move apart, while the gas is extracted simultaneously from the spaces separating the layers under the effect of the vacuum transmitted by the rubber frame. After the gas has been extracted from the spaces separating the various layers, the temperature is increased and the pressure in the vacuum box is brought to atmospheric pressure, while the pressure in the rubber frame remains, during this time, at a level below atmospheric pressure.
Document DE-2,209,643 C3 also describes a process for the manufacture of laminated glass which does not require autoclaving and which is suitable for a continuous production cycle. In this known process too, the pack of layers is surrounded by an elastomeric sealed profiled frame through which the air and gas present between the layers are sucked out, while the pack of layers is subjected simultaneously to an external vacuum in a vacuum box. In this case, the pack of layers is heated at the same time as being put under vacuum, and is subsequently brought to atmospheric pressure, while still being heated, and bonded in this situation.
These known processes involve two separate vacuum systems and require a frame in order to seal the edge of the pack of layers not only during the phase of creating the vacuum but also during the following phase of assembly at atmospheric pressure.
The object of the invention is to simplify further a process of this kind so as to be able to integrate it even better in a continuous manufacturing process,
According to the invention, this object is achieved by the fact that the pack of layers is first of all heated to a temperature close to the softening temperature of the thermoplastic polymer, that the gas is extracted directly from the spaces separating the layers of the pack of layers, due to the effect of the vacuum which exists inside the vacuum box, through those edges of the pack of layers which are not covered and that, after completing the extraction of the gas inside the vacuum box, the vacuum being maintained, the edge of the pack of layers is, for the purpose of sealing it, bonded by means of mechanical pressure exerted around the edge of the pack of layers.
The process according to the invention consequently requires neither an additional sealed profiled frame, the shape and size of which depends moreover on each glazing model, nor an additional means for separate suction through these sealed profiled frames. Rather the invention exploits the observation that better removal of air and better extraction of gas from the spaces separating the layers are achieved when the pack of layers is subjected merely to the vacuum in the vacuum box without any clamping or retaining components around its edge. This is because the film used as thermoplastic interlayer is provided with a surface structure. As the pack of layers is being preheated up to a level close to the softening temperature of the thermoplastic interlayer, the layers are not yet completely bonded to each other because of its surface structure, and thus the contact surface between the structured film and the adjacent layers is sufficiently permeable to allow effective air removal and gas extraction simply by the effect of the external vacuum.
Moreover, given that the temperature of the pack of layers is already sufficiently high at this moment to cause a sealed bond with the surface of the glass due to the effect of sufficiently high mechanical pressure, good sealing around the edges is achieved by means of the subsequent mechanical pressing operation, which is limited to the immediate marginal region of the external layers. The atmospheric pressure which is subsequently exerted on the pack of layers thus sealed around their edges has the effect of pressing the layers against each other over their entire surface.
This treatment is simply followed by an additional heat treatment at atmospheric pressure in which the thermoplastic polymer of the interlayer is further softened and the ultimate transparency of the pane of laminated glass is achieved by complete impregnation of the glass surfaces.
According to another variant, the invention does not exclude, after bringing the laminate to atmospheric pressure and optionally after the additional heat treatment at atmospheric pressure, passing the laminate into an autoclave where it is subjected to a high overpressure. According to this variant of the invention, the time spent in the autoclave is advantageously less than that of the known techniques.